Aircraft components including items such as wing skins and other panels are increasingly being made from composite materials, for example laminates. Direct attachment of leading and trailing edge structures, such as leading and trailing edge panels, to the wing skin is often impractical when using laminates. Pre-moulded precision-fit joints, known as joggles, are difficult to manufacture in thick laminates, would increase overhang size and may adversely affect the mechanical properties of the laminate. Furthermore, it is difficult to provide effective panel attachment through thick laminates.
It is known to fasten the leading and trailing edge panels of a wing to the wing skin using butt-straps located along the joint between the leading and trailing edges panels and the wing skin. These butt-straps secure the panels in place and ensure that the leading and trailing edges of the panels are properly aligned with the corresponding trailing and leading edges of the wing skin.
Conventionally, a metallic butt-strap 10 is used as shown in cross-section in FIG. 1. The butt-strap is attached to the inner mould line (IML) face of the wing skin that generally faces towards the interior of the wing. Prior art butt-strap 10 has a stepped, z-shaped profile, with a short vertical portion 10a joining two horizontal plate portions 10b,c. In this example, plate 10b fits over a portion of the IML face of cover 20 of the aircraft's wing skin such that the leading edge of cover 20 butts up against vertical portion 10a. This is bolted in place with bolt 30 that is countersunk into cover 20 on its outer-mould-line (OML) face.
Plate 10c is attached to the structure that is to be fixed to the leading edge of the cover. For example a “D”-nose leading edge skin 40 is shown attached to a wing cover leading edge 50 (FIG. 2). In order to reduce erosion of the composite skin 20 by airflow 60, the “D”-nose skin 40 is usually chosen to be sufficiently thick to overhang the leading edge 50 of cover 20. However, it is found that aerodynamic erosion still occurs and the increased thickness also increases drag. Aerodynamic erosion is often exacerbated when composite materials are used.
The prior-art butt-strap is also vulnerable to bird strike and similar collisions. FIG. 3 shows schematically how an impact on the leading-edge structure (not shown) attached by butt-strap 10 can lead to catastrophic forces on bolt 30.
The present invention seeks to ameliorate at least some of the abovementioned problems.